1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus.
2. Description of the Related Art
In a conventional magnetic disk apparatus of sector servo type, data tracks are used to record data in a magnetic disk as a recording medium, and arranged on a plurality of concentric circles. The data tracks each are also called a "cylinder". Each cylinder has a plurality of sectors. Each of the sectors has a servo area and a data area. Servo data is recorded in the servo area, and data to be read/written by a user is recorded in the data area. The servo data includes servo detection data for detecting the servo area, address code data for distinguishing the cylinder, and burst data for positioning a magnetic head on the center of the cylinder. The servo detection data has a signal pattern which is not used in the data to be read/written in the data area by a user. In the signal pattern, data in which no magnetization reverse occurs, i.e., continuous erase data, is recorded.
FIG. 1A shows a part of the servo area in each sector of the recording medium. In the figure, a magnetization direction of recorded data is not shown. Vertical lines indicate magnetization reverse locations of the recorded data. The servo detection data is recorded in a portion called an erase area, and the address code data is recorded in a portion called an address code area. FIG. 1B shows a reproduced signal waveform obtained when the magnetic head is located at cylinder number 0 of the recording medium.
In general, the determination of address code data "0" or "1" is performed on the basis of the presence/absence of a dibit. The dibit means that two reproduced signals, each having positive or negative polarities, are generated by two magnetization changes occurring in a predetermined time period. If the dibit is present, the address code data is "1". If the dibit is absent, the address code data is "0". The address code data "0" and "1" are modulated by a modulation method capable of obtaining modulation data "00" and "11", as shown in FIG. 2, and the modulation data is recorded on the recording medium as NRZ (non return to zero) data, as shown in FIG. 3.
If the address code data "0" is continuously recorded on the address code area, it is difficult to distinguish the address code data from the servo detection data including the erase data. However, if the address code data "0" is recorded so as not to be continuous, the relationship between the address code data and cylinder number becomes complex and much time is required to convert the address code data into cylinder number. In addition, if the data length of the address code data is long, the servo area in each sector increases and accordingly the data area decreases. That is, the recording capacity of the recording medium for data which a user can read/write is decreased.
In the modulation method capable of obtaining the modulation data, as shown in FIG. 2, since a peak shift amount of a readout signal output from the magnetic head is large, the error rate increases in relation to the determination of the address code data "0" and "1". However, if the recording frequency is decreased to prevent the increase of the error rate, the servo area increases, as stated above, and the recording capacity of the recording medium for data which a user can read/write decreases.
Under the circumstances, there has been a demand for a magnetic recording and reproducing apparatus capable of converting the address code data to the cylinder number at high speed, reducing the peak shift amount, and decreasing the servo area.